This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-272211, filed Sep. 7, 2000; and No. 2001-218528, filed Jul. 18, 2001, the entire contents of both of which are incorporated herein by
1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, particularly, to a semiconductor device including a copper wiring and a method of manufacturing the same.
2. Description of the Related Art
In the conventional semiconductor device, aluminum is widely used as the material of the wiring. In recent years, copper having a lower resistivity and cheaper has come to be used as a wiring material in place of aluminum. However, if a Cu wiring is subjected to a heat treatment in an atmosphere containing oxygen, oxidation of the Cu wiring surface proceeds, with the result that the resistance of the wiring is markedly increased.
FIGS. 1A to 1C are cross sectional views schematically showing a conventional process of forming a multilayer interconnection structure. As shown in FIG. 1A, a first interlayer insulation film 13 is formed on a semiconductor substrate 2, and a first Cu wiring 14 is buried in the insulation film 13. Incidentally, the Cu wiring 14 is the one which contains mainly Cu and has a layer or layers containing a material such as Ta, TaN, Ti or TiN on the sidewalls and bottom surface thereof.
In the conventional process, an interlayer insulation film 23 is formed as a continuous film on the insulation film 13 and the wiring layer 14, followed by forming a resist pattern 5 on the insulation film 23, as shown in FIG. 1A. It is noted that interlayer insulation film has a single-layer or a multi-layer structure and includes a film such as a silicon nitride film (herein after referred to as xe2x80x9cSiN filmxe2x80x9d), silicon oxide film, organosilicon film or organic insulation film. In the next step, a groove for a second Cu wiring is formed in the insulation film 23 by a reactive ion etching (hereinafter referred to as xe2x80x9cRIExe2x80x9d) by using the resist pattern 5 as a mask, as shown in FIG. 1B. Incidentally, the Cu wiring 14 is exposed to the outside for the via contact in a part of the bottom surface of the groove formed in the insulation film 23. Then, the resist pattern 5 is removed by the ashing in an atmosphere containing oxygen. In this step, the uncovered portion of the Cu wiring 14, which is exposed to oxygen at a high temperature, is oxidized so as to form an oxide film 14a made of, for example, Cu2O, as shown in FIG. 1C. By the oxidation of Cu into Cu2O, the Cu2O layer is expanded to a volume 1.65 times as much as the original Cu layer. As a result, where the oxide film 14a is formed as shown in FIG. 1C, cracks tend to be generated around the oxide film 14a. 
A similar problem also takes place in the case where copper is used as a material of an electrode such as a bonding pad.
FIGS. 2A and 2B are cross sectional views schematically showing a conventional bonding process. In FIG. 2A, an interlayer insulation film 13 is formed on the semiconductor substrate 2, and a bonding pad 4 made of copper is buried in the insulation film 13. Further, an SiN film 6 and an insulation film 23 are successively formed on the insulation film 13.
The bonding of an Au wire to the pad 4 shown in FIG. 2A is carried out generally in the air atmosphere under the state that the substrate 2 is heated to a high temperature. Therefore, the surface of the pad 4 is exposed to a high temperature oxygen so as to be oxidized, resulting in formation of an oxide film 4a made of, for example, Cu2O. It follows that cracks are generated around the pad 4 so as to cause a peeling problem in some cases.
The process shown in FIGS. 3A to 3F and the process shown in FIGS. 4A to 4C are known to the art as the process for preventing the occurrence of the cracks described above with reference to FIGS. 1A to 1C, 2A and 2B.
FIGS. 3A to 3F are cross sectional views schematically showing another conventional process of forming a multilayer interconnection structure. In the conventional process, a Cu wiring 14 is formed first as shown in FIG. 3A, followed by forming an SiN film 16, an interlayer insulation film 23 and a resist pattern 5, as shown in FIG. 3B. Then, a groove is formed in the insulation film 23 by RIE with the resist pattern 5 used as a mask, as shown in FIG. 3C. In this etching step, the SiN film 16 plays the role of an etching stopper. Then, the resist pattern 5 is removed by the ashing carried out in an atmosphere containing oxygen 11, as shown in FIG. 3D. In the next step, that portion of the SiN film 16 which is positioned within the groove is removed by etching as shown in FIG. 3E, followed by filling the groove with copper to form a Cu wiring 24, as shown in FIG. 3F. According to this process, the Cu wiring 14 is covered with the SiN film 16 and, thus, is not oxidized in the ashing step. It follows that it is possible to prevent the crack occurrence.
FIGS. 4A to 4C are cross sectional views schematically showing another conventional bonding process. In this process, the interlayer insulation film 13, the bonding pad 4 made of copper, the SiN film 6, and the insulation film 23 are formed successively on the semiconductor substrate 2, as shown in FIG. 4A. In the next step, an aluminum electrode 7 is formed to cover the side walls and the bottom surface of the groove formed in the SiN film 6 and the insulation film 23, as shown in FIG. 4B. Then, an Au wire 8 is bonded to the electrode 7, as shown in FIG. 4C. It should be noted that, in this process, the bonding pad 4 within the groove is covered with the aluminum electrode 7, with the result that the bonding pad 4 is not oxidized in the bonding step of the Au wire 8.
As described above, in the process shown in FIGS. 1A to 1C and in the process shown in FIGS. 2A and 2B, the surfaces of the Cu wiring 14 and the Cu pad are oxidized. In contrast to the processes, it is possible to prevent the surfaces of the Cu wiring 14 and the Cu pad 4 from being oxidized in the processes described with reference to FIGS. 3A to 3F and to FIGS. 4A to 4C. On the other hand, however, required are additional step of forming the SiN film 16, the etching step and the step of forming the Al electrode 7.
It is possible for another problem to occur in accordance with oxidation of the Cu wiring and the Cu pad. For example, if a potential difference is generated between the Cu wiring and the interlayer insulation film, copper oxide tends to be ionized so as to be diffused into the insulation film. Such a diffusion brings about increases in the wiring resistance and in the wiring capacitance. In general, an SiN film or an SiCH film is formed as a diffusion barrier film by a chemical vapor deposition (hereinafter referred to as xe2x80x9cCVDxe2x80x9d) on the surface of the interlayer insulation film in which is buried the Cu wiring. What should be noted is that it is difficult for the bonding strength between the SiN film or the SiCH film and the copper oxide film to be maintained in a satisfactory state.
It is possible to suppress the problem accompanying the oxidation of the Cu wiring by applying a surface treatment to the Cu wire by utilizing a plasma using, for example, an NH3 gas or an H2 gas as the raw material. However, such a plasma processing gives rise to the problem described below.
In the conventional semiconductor device having a multilayer interconnection structure, a silicon oxide film having a relative dielectric constant xcexa of about 4.1 was used in general as an interlayer insulation film. In recent years, vigorous studies are being made in an attempt to put into practical use a multilayer interconnection structure in which an organosilicon film or an organic film having a relative dielectric constant xcexa of about 4.1 is used as the interlayer insulation film and copper is used as a material of the wiring. According to the particular construction, it is possible to suppress both the wiring resistance and the wiring capacitance.
However, where the plasma processing noted above is applied to the organosilicon film or the organic film, the organic components are migrated out of the surface region of the organosilicon film or the organic film, with the result that the surface region forms a brittle denatured layer. The denatured layer lowers the bonding strength between the interlayer insulation film and the diffusion barrier film to cause, in the subsequent heat treating step, a peeling of the diffusion barrier film from the interlayer insulation film. Also, the denatured layer tends to adsorb water easily. Since the insulation film absorbing water tends to exhibit a high dielectric constant, formation of the denatured layer impairs the effect of suppressing the wiring capacitance. In addition, since the insulation film absorbing water generates a gas in the heat treating step, the peeling of the diffusion barrier film is promoted.
What should also be noted is that, where the diffusion barrier film is formed by a coating method, it is difficult to carry out the plasma processing and the formation of the diffusion barrier film successively under vacuum. It follows that, even if the surface of the Cu wiring is reduced by the plasma processing, the surface of the Cu wiring is oxidized again. If an oxide film is formed on the surface of the Cu wiring, the wiring resistance is increased by the increase in the surface resistance. In addition, the wiring capacitance is also increased.
According to a first aspect of the present invention, there is provided a semiconductor device comprising a semiconductor substrate and a conductive layer above the semiconductor substrate, wherein the conductive layer contains copper, a surface region of the conductive layer contains at least one of Cxe2x80x94H bonds and Cxe2x80x94C bonds, and a total amount of C atoms forming the Cxe2x80x94H bonds and C atoms forming the Cxe2x80x94C bonds in the surface region is 30 atomic % or more of a whole amount of elements in the surface region.
According to a second aspect of the present invention, there is provided a semiconductor device comprising a semiconductor substrate and a conductive layer above the semiconductor substrate, wherein the conductive layer contains copper, and a surface of the conductive layer is provided with particles each of which contains carbon.
According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising, forming a first conductive layer containing copper above a semiconductor substrate, supplying a surface of the first conductive layer with a substance containing carbon, and forming a second conductive layer on the surface of the first conductive layer on which carbon originating from the substance remains.
According to a fourth aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising, forming a conductive layer on a first insulation layer containing carbon, the first insulation layer being supported by a semiconductor substrate, treating exposed surfaces of the conductive layer and the first insulation layer with a plasma containing carbon, and forming a second insulation layer on the conductive layer and the first insulation layer after the treatment of the surfaces with the plasma.